Express CBD and CAD in radian measure. Then we find the segment of each of the circles cut off by the chord CD, by taking the area of the sector of the circle BCD and subtracting the area of triangle BCD.
Similarly we find the area of the sector ACD and subtract the area of triangle ACD.

Remember that for the area of the sectors you must have CBD and CAD in radians.

One more thing if the two circles are of the SAME radius please note that the area is symmetrical about the chord CD. Therefore, you only need to find the area in one half of the intersection and multiply by 2.

A shorter equation is

Area = 2 * ( ( 1/2 ) ( CBD ) r1 ^ 2 - ( 1/2 ) r1 ^ 2.sin( CBD ) ).

One more derivation if the redis is equal then you can find out using, this formulaArea = r^2*(q - sin(q)) where q = 2*acos(c/2r),
where c = distance between centers and r is the common radius.

I think now you can solve this. If something goes wrong, then post in the comments.